This invention is in the field of stents for maintaining patency of any one of a multiplicity of vessels of the human body.
In the last decade, many different designs of stents have been used to maintain patency of arteries and other vessels of the human body. In all such devices, hoop strength is an important characteristic. Specifically, the stent must have enough hoop strength to resist the elastic recoil exerted by the vessel into which the stent is placed. The Mass stent described in the U.S. Pat. No. 4,553,545 and the Dotter stent described in U.S. Pat. No. 4,503,569 are each open helical coils. The Palmaz stent described in the U.S. Pat. No. 4,733,665 is of the xe2x80x9cchinese fingerxe2x80x9d design. The Gianturco-Rubin stent currently sold by Cook, Inc. is another stent design which like the stents of Mass, Dotter and Palmaz does not have any closed circular member to optimize hoop strength.
The ideal arterial stent utilizes a minimum wire size of the stent elements to minimize thrombosis at the stent site after implantation. The ideal arterial stent also posses sufficient hoop strength to resist elastic recoil of the artery. Although the optimum design for maximizing hoop strength is a closed circular structure, no prior art stent has been described which has a small diameter when percutaneously inserted into a vessel and which expands into the form of multiplicity of closed circular structures (i.e. rings) when expanded outward against the vessel wall.
The present invention is an expandable stent that can be used in an artery or any other vessel of the human body which, when expanded, forms a mutiplicity of generally circular rings whose closed structure optimizes hoop strength so as to minimize elastic recoil of the vessel into which the stent is inserted. Furthermore, the structure of the stent in the present invention is initially in the form of folded ellipses or ovals which can be formed to a small diameter for percutaneous insertion by means of a stent delivery catheter. The ovals are joined to each other by either a straight or undulating shaped wires which are called xe2x80x9clongitudinalsxe2x80x9d which serve to space the deployed rings within the vessel. Straight longitudinals are used in straight vessels and undulating longitudinals can be employed in either straight or highly curved vessels such as some coronary arteries.
Thus, an object of this invention is to provide a stent having a maximum hoop strength by the employment of closed, generally circular structures which are in fact rings.
Another object of this invention is that the rings are initially in the form of ovals that can be folded to fit onto a cylindrical structure at a distal portion of a stent delivery catheter.
Still another object of this invention is that the fully deployed rings are spaced apart by means of longitudinals which are either straight of undulating wires that are placed to be generally parallel to the longitudinal axis of the vessel into which the stent is deployed.
Still another object of this invention is that the pre-deployment stent structure is formed as a single piece out of a metal tube having a smaller inside diameter as compared to the outside diameter of an expandable balloon onto which the pre-eployment stent is mounted.
These and other important objects and advantages of this invention will become apparent from the detailed description of the invention and the associated drawings provided herein.